Denmark brands mystery drone flights 'serious' attack

"This is part of the development we have recently observed with other drone attacks, airspace violations, and cyberattacks targeting European airports," Frederiksen said in a statement sent to AFP.

She referred to similar drone incidents in Poland and Romania and the violation by Russian fighter jets of Estonia's airspace, which have raised tensions in light of Russia's ongoing invasion of Ukraine.

The governments of Poland, Estonia and Romania have pointed the finger at Moscow, which has brushed off the allegations.

Frederiksen told Danish broadcaster DR she could "not rule out" that Russia was behind the drone activity.

Moscow denied involvement, with Kremlin spokesman Dmitry Peskov dismissing Frederiksen's comments as "unfounded accusations".

- NATO warns Russia -

Copenhagen police inspector Jens Jespersen said "several large drones" flew over the Copenhagen airport for more than three hours on Monday evening.

Police decided not to shoot down the drones for safety reasons.

Jespersen told DR it was not known where the drones were being controlled from, but that it could have been from many kilometres away, possibly "from a ship".

"The number, size, flight patterns, time over the airport. All this together... indicates that it is a capable actor. Which capable actor, I do not know," Copenhagen police inspector Jens Jespersen told reporters.

"It was an actor that had the capacity, the will and the tools to make their presence known."

NATO said it was "too early to say" whether Russia was responsible, but warned Moscow to stop an "escalatory" pattern of airspace violations along its eastern flank.

Ukrainian President Volodymyr Zelensky denounced what he called a Russian violation of Denmark's airspace, in a message on X.

- 'High threat of sabotage' -

Danish intelligence said the Scandinavian country was facing a "high threat of sabotage".

"Someone may not necessarily want to attack us, but rather stress us out and see how we react," said Flemming Drejer, director of operations at Denmark's intelligence service PET.

Frederiksen said in a post on Facebook that she had spoken Tuesday with the prime ministers of neighbouring Norway and Sweden, NATO's secretary general, the head of the European Council and EU chief Ursula von der Leyen.

The drones incident came a week after Denmark announced it would acquire long-range precision weapons for the first time, citing the need to be able to hit distant targets as Russia would pose a threat "for years to come".

Moscow's ambassador to Copenhagen Vladimir Barbin had called the statement "pure madness".

"No one, anywhere, ever in the world has considered threatening a nuclear power publicly. These statements will undoubtedly be taken into account," he warned in a statement on Telegram.

- Air traffic disruptions -

Airport officials said some 30,000 passengers were affected Tuesday by flight diversions and cancellations, but air traffic was returning to normal late Tuesday afternoon.

Copenhagen police said they were cooperating with colleagues in Oslo after drone sightings also caused the airport in the Norwegian capital to close for several hours.

"We had two different drone sightings," Oslo airport spokeswoman Monica Fasting told AFP, adding that 14 flights were diverted.

Norwegian police had yet to comment on the drone incident overnight, but the country's intelligence service PST told AFP it was involved in the investigation.

Norway's government on Tuesday said Russia had violated its airspace three times this year -- in April, July and August -- after a decade without any similar incidents.

"This is not acceptable," Prime Minister Jonas Gahr Store said in a statement.

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